Group III-V compound (i.e. compound consisting of elements of groups III and V) semiconductor materials, with gallium arsenide (GaAs) as a representative, find wide use in the fields of satellite communication, microwave devices, laser devices and light-emitting diodes, owing to their unique electronic properties. In the production of devices like Heterojunction Bipolar Transistors (HBT), High Electron Mobility Transistors (HEMT) and LED, substrates with high-quality surfaces are required for the growth of quantum well structures on the surfaces by molecular beam epitaxy (MBE) technology or metal organic compound vapor deposit (MOCVD) technology. With the manufacturing processes of semiconductor devices improving, the devices are getting smaller and smaller in size, while becoming more and more efficient in use; the devices in terms of reliability and stability rely more and more on the quality of the semiconductor substrate, especially the quality of the wafer surface.
Cleaning is the last and the key operation to get a high quality surface in the wafer manufacturing process; it is intended to remove various residues derived from the preceding operations, so as to get a fresh clean surface, serving as the basis of subsequent operations. For now, the compound semiconductors are still cleaned mostly by the established method for cleaning monocrystal silicon wafer developed by RCA (Radio Corporation of America) in 1970, i.e. cleaned by using a mixture of ammonia, hydrogen peroxide and water (APM or SC-1) and a mixture of hydrochloric acid, hydrogen peroxide and water (HPM or SC-2), aided with various physical effects and mechanical operations.
Gallium Arsenide, a binary compound semiconductor, has physical and chemical properties widely different from silicon monocrystal. The surface of Gallium Arsenide wafer is formed of gallium atoms and arsenic atoms. Owing to different chemical properties of gallium and arsenic, its surface reactivity is different: the native oxide layer thereof consists of gallium dioxide (Ga2O3), arsenic trioxide (As2O3), arsenic pentoxide (As2O5) and a small amount of elemental arsenic (As). The conventionally used SC-1 and SC-2 have very obvious corrosive effect on gallium arsenide, and thus if the method for cleaning silicon wafer is directly adopted without modification, phenomena like rough surface (fogging), non-uniform corrosion, and concentration of foreign particles would easily occur. Such surface will bring about problems such as abnormal growth, anomaly structures and increased defects of epitaxy layers in the subsequent epitaxy application.